Puerto Rico Coastal Hazards Mapping

1. Puerto Rico Coastal Hazards Mapping By David M. Bush State University of West Georgia

2. The original source of much of this information is: Bush, David M., Bruce R. Richmond, and William J. Neal, 2001. Coastal Zone Hazard Maps: Eastern Puerto Rico. Environmental Geosciences, 8(1), p. 38-60.

3. Puerto Rico Coastal Hazards Maps • Goal—to develop a tool for quick visualization of multiple coastal hazards • A basis for hazard mitigation and management recommendations • To be of use to: • Coastal planners • Managers • Property owners • Potential property owners

4. PR Shoreline Setting • Compartmentalized • Geologic/oceanographic processes and hazards can be considered on a compartment-by-compartment basis • Highly developed in places

5. Six Types of Hazards Considered • Shoreline-setting hazards (long-term problems) • Marine hazards (short-term impacts of storms) • Earthquake and slope hazards (ground shaking, landslides, liquefaction) • Riverine hazards (historical floods) • Development hazards (high-density or dangerous settings) • Engineering hazards (stabilization, nourishment, sand mining)

6. Puerto Rico is the smallest and easternmost of the Greater Antilles

7. The insular shelf around Puerto Rico is variable, but very narrow on the north.

8. A side-looking airborne radar (SLAR) image clearly shows the physiography of the 150 x 50-km island of Puerto Rico. Several small rivers drain to the north, and the northern coastal lowlands are wide compared to the southern. Courtesy of Simulation Systems, Inc.

9. Natural Hazards(after Bryant, 1991) Of the top 25 natural hazards, those affecting coasts: 2. Tropical cyclones 6. Extratropical storm 7. Tsunami 8. Sea-level rise 10. Beach erosion 13. Ocean waves 14. Localized strong wind 15. Subsidence

10. Examples of Natural Hazards Affecting Puerto Rico • Landslides—from rainfall and earthquakes • Waves and surge from winter storms • Hurricanes and tropical storms • Rainfall • Overwash • Erosion • Flooding • Wind • Rainfall from tropical waves

11. NOAA satellite image of Hugo nearing Puerto Rico

12. Hugo 1989 Major hurricanes affecting Puerto Rico seem to follow one of two main paths. Hugo is #13.

13. USGS figure of path of the eye of Hurricane Hugo as it crossed the Virgin Islands and Puerto Rico

14. St. Croix San Juan National Weather Service radar positions of Hugo’s eye. Note irregular path of storm center when viewed in detail. Also note the deflection (loop) in the path which resulted in an extended battering of St. Croix.

15. Direct wave impact on first row of buildings, Condado area of San Juan

16. Sand washover along the Piones shoreline after Hurricane Hugo. An estimated 500,000 cubic meters of sand was washed ashore along this stretch (Bush, 1991).

17. Overwash from Hugo extended several kilometers along the Puerto Rico shoreline and extended 10’s of meters inland. From Bush (1991).

18. Post-Hugo field study estimated storm surge along several coastal reaches. From Bush, 1991

19. Hugo was a relatively dry hurricane and caused only local flooding as here at the Ro de la Plata mouth.

20. Hugo caused hundreds of small landslides in the mountains of Puerto Rico.

21. USGS map showing landslide susceptibility in the municipality of Comero, Puerto Rico.

22. Swell from North Atlantic winter storms cause the largest waves hitting the northern coast of Puerto Rico. Here are tracks of several storms studied by Fields and Jordan (1972).

23. The 1991 Halloween Nor’easter caused storm-wave swash flooding and overwash along the northern coast of Puerto Rico as here in Isabela. Photo taken January 1992

24. Three Kings Day storm, 1992, Puerto Rico, 24-hour rainfall totals for selected areas. From El Nuevo Da newspaper.

25. Flash flood from 1992 Three Kings Day flood, PR

26. Coastal Erosion • Another major natural hazard in Puerto Rico • Many ways to measure • A simple way is a “geoindicators” assessment (Bush et al., 1999)

27. Geoindicators of Erosion • Dunes scarped or breached • Bluffs steep with no talus ramp • Peat, mud, or tree stumps exposed on beach • Beach narrow or no high-tide beach • Overwash passes or fans • Vegetation ephemeral or toppled along scarp line

28. Geoindicators of Severe Erosion • Dunes absent with overwash common • Active wave scarping of bluffs or dune remnants • Tidal channels exposed in surf zone • Vegetation absent • Engineering structures now on beach or offshore

29. Geoindicators of Accretion or Long-Term Stability • Dunes and beach ridges robust, unbreached, vegetated • Bluffs vegetated with stable (vegetated) ramp at toe • Overwash absent • Vegetation well-developed from interior maritime forest, to dune shrubs, and pioneer beach grass

30. Erosion rates for Puerto Rico were calculated in detail from aerial photography by Thieler and Danforth (1993).

31. Beach and dune sand mining may be the greatest contributor to coastal erosion in the Caribbean.

32. 1977 photo of impact of beach sand mining in Puerto Rico

33. Tap roots of pine trees left stranded by erosion (1991 photo). Beach sand mining along the Piones shoreline in Puerto Rico to build the international airport contributed to a severe erosion problem culminating in a massive seawall built in 2000.

34. Aerial view of Piones area taken after Hurricane Hugo (1989). Sand mining created a severe erosion problem.

35. Artificial dunes were built in the mid 1980’s to combat the Piones erosion problem. Swell from a January, 1988 winter storm removed most of the dunes. The poles had been covered by over 10 feet of sand.

36. Another source of erosion information in Puerto Rico is a qualitative discussion by Morelock (1978). White bars show his critical erosion areas. XXX’s are seawalls.

37. Condado Lagoon As in many places, a major contributor to coastal hazard problems is overbuilding at the coast. Here is the Condado sector of San Juan.

38. La Perla The walled city of Old San Juan sits safely high atop an eolianite ridge A squatter development called La Perla built outside the walls on the slopes of the ridge places many homes and people in a hazardous location.

39. Seismic Hazards • Puerto Rico sits amid several active Caribbean and Atlantic tectonic zones • Hazards include ground shaking, liquefaction potential, and tsunamis

40. Generalized tectonic setting. From McCann (1984)

41. From McCann (1984)

42. October 1918 Mona Passage earthquake, Modified Mercalli Scale. From McCann (1984). Mercalli Scale of V can be enough to cause liquefaction in which case all major metropolitan areas of Puerto Rico are at risk.

43. Damage in Mayagez from the 1917 earthquake. Photo courtesy of the Puerto Rico archives.

44. Damage in Mayagez from the 1917 earthquake. Photo courtesy of the Puerto Rico archives.

45. Modified Mercalli Scale from November 1867 Virgin Islands earthquake.

46. Much of the metropolitan San Juan development is on artificial fill emplaced before or without strict codes or enforcement. A disaster waiting to happen.

47. Tropical weathering provides unstable material easily destabilized by ground shaking during an earthquake or by intense rains.

48. Notches cut into the weathered hillside for home sites create oversteepened slopes with increased potential for landslides.

49. Some slope stabilization efforts have been undertaken such as in this example from the Luquillo National Forest.

50. Hazard Categories considered in coastal hazard map preparation • Shoreline Setting Hazards • Marine Hazards • Slope and Seismic Hazards • Riverine Hazards • Development Hazards • Engineering Hazards